Overview
Atrioventricular (AV) block occurs due to delayed conduction of an impulse between the atria or ventricles, due to intrinsic or extrinsic causes.
Pathogenesis
Causes of Atrioventricular (AV) Block
Intrinsic
- Idiopathic degeneration
- Myocardial infarction
- Congenital - congenital heart disease, neonatal lupus
- Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
- Cardiac procedures - valvular surgery, correction of congenital heart disease, catheter ablation
- Systemic lupus erythematosus
- Myocarditis
Extrinsic
- Physiologic - sleep, athletes
- Autonomic - carotid sinus massage, carotid sinus hypersensitivity
- Drugs - beta blockers, calcium channel blockers, digoxin, adenosine, amiodarone
- Hyperkalaemia
- Hypothyroidism
Physiologic and autonomic causes of AV block tend to result in first degree or Mobitz I heart block, while pathologic causes tend to result in Mobitz II, advanced second degree or complete heart block.
Diagnosis
ECG Findings
- 1st degree - prolonged PR interval >200ms (5mm)
- 2nd degree: type I Mobitz (Wenckebach) - initial normal PR interval with progressive prolongation of PR interval followed by a dropped QRS complex.
- 2nd degree: type II Mobitz - constant PR interval with intermittently dropped QRS complexes
- 2nd degree: advanced - two or more consecutive P waves without QRS complexes; may be in a 3:1, 4:1 or higher pattern
- 3rd degree - complete dissociation of P waves and QRS complexes
Examples
- 1st degree AV block
![1st degree AV block]()
- 2nd degree AV block: type I Mobitz
![2nd degree AV block type I Mobitz]()
- 2nd degree AV block: type II Mobitz
![2nd degree AV block type II Mobitz]()
- Advanced 2nd degree AV block
![Advanced 2nd degree AV block]()
- 3rd degree AV block
![3rd degree AV block]()
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